Plastically worked cast aluminum alloy product, a manufacturing method thereof and a coupling method using plastic deformation thereof

ABSTRACT

The newly proposed cast aluminum alloy product has the composition consisting of 6.5-8.0% Si, 0.25-0.45% Mg, 0.08-0.40% Fe, 0.001-0.01% Ca, P less than 0.001%, 0.02-0.1% Ti, 0.001-0.01% B, optionally one or two of 0.05-0.3% Cr and 0.05-0.2% Mn, and the balance being Al except inevitable impurities. It has the metallurgical structure that an α-Al phase in a surface layer is of average grain size different by 50 μm or less from an α-Al phase in an inner part, and that a maximum size of eutectic Si particles is 400 μm or smaller. It is manufactured by injecting a molten aluminum alloy into metal dies at an injection speed of 0.05-0.25 m/second, and then cooling the injected alloy at a cooling speed of 20° C./or higher in a temperature range between liquidus and solidus curves in a state charged with a pressure of 30 MPa or higher. Since the cast product is good of ductility, it is used as a member for coupling another member therewith by calking or the like.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a cast aluminum alloy product towhich another member can be coupled by plastic deformation such ascalking, a method of manufacturing thereof and also a coupling methodusing plastic deformation thereof.

[0002] A part, such as a protector in a braking system for an automobileenclosing a hydraulic circuit therein, has a regulator at an outlet ofthe hydraulic circuit for regulating a flow rate of oil. Since theregulator is generally made of steel or synthetic resin, which can notbe fixed to the aluminum protector by welding, plastic deformation (e.g.calking) of the aluminum member has been adopted for fixing theregulator.

[0003] The aluminum protector for a braking system of an automobile isestimated to be plastically deformed for fixing other members, asmentioned above. In this regard, such a wrought alloy as Al—Si—Mgrelatively high of toughness has been used so far for such the purpose.However, since the wrought alloy is relatively expensive compared with acast alloy, it is expected to provide a protector made of a cheap castalloy.

[0004] A cast aluminum alloy product generally includes such castdefects as blowholes and comprises a metallurgical structure whereinα-Al phase comes out as a matrix with ununiform grain size. Segregationof an eutectic Si phase grown to a coarse size as well as dispersion ofprimary Si are often observed in the matrix. Due to such themetallurgical structure, the cast aluminum alloy product is poor ofductility and so regarded as a member improper to be coupled withanother member by plastic deformation.

[0005] In actual, JP 6-145866A discloses a cast aluminum alloy productfor use as a protector of an automobile braking system, whereby growthof isometric crystals is promoted by addition of Ti and B to reduceoccurrence of blowholes. Even the proposed aluminum alloy product isinsufficient of ductility, so it can not be yet used as a member to becoupled with another member.

SUMMARY OF THE INVENTION

[0006] The present invention aims at provision of a cast aluminum alloyproduct useful as a member to be coupled with another member by suchplastic deformation as calking without defects as above-mentioned. Thecast product is improved in ductility by addition of Ca, Ti and B withreduction of P content and by size-control of α-Al grains and eutecticparticles.

[0007] The newly proposed cast aluminum alloy product has thecomposition consisting of 6.5-8.0 mass % Si, 0.25-0.45 mass % Mg,0.08-0.40 mass % Fe, 0.001-0.01 mass % Ca, P less than 0.0015 mass %,0.02-0.1 mass % Ti, 0.001-0.01 mass % B, optionally one or two of0.05-0.3 mass % Cr and 0.05-0.2 mass % Mn, and the balance being Alexcept inevitable impurities. The cast aluminum alloy product has themetallurgical structure that an α-Al phase grain in a surface layer froma surface to a depth of 1 mm is of average grain size different by 50 μmor less from an α-Al phase grain in an inner part, and an eutectic Siphase is controlled at a particle size of 400 μm or smaller.

[0008] Another member is coupled to the cast aluminum alloy product bypartial plastic deformation of the cast aluminum alloy product.

[0009] After a molten aluminum alloy is adjusted to the specifiedcomposition, it is injected into a cavity of metal dies at a speed of0.05-0.25 m/second and then cooled at a cooling speed of 20° C./secondor higher in a temperature range between liquidus and solidus curves ina state charged with a pressure of 30 MPa or higher.

[0010] A cast body has a cave or hole for coupling another memberthereto. The mating member can be coupled to the cast aluminum alloyproduct by arranging the mating member in the cave or hole and thenplastically deforming a part above or around the cave or hole so as torealize metal flow to the cave or hole.

[0011] A cast aluminum alloy product generally includes cast defectssuch as blowholes and segregates of an eutectic phase grown to a coarseparticle, with big difference in average grain size of an α-Al phasebetween a surface layer and an inner part. The big difference in averagegrain size, cast defects and segregation of the eutectic Si phase causepartial decrease of elongation of the cast aluminum alloy product,resulting in irregularity of elongation or plastic deformation as wellas cracking, so that the cast aluminum alloy product is not regarded asa member suitable to be coupled with another member.

[0012] The inventors have researched and examined effects of differencein average grain size, cast defects and segregation on ductility fromvarious aspects, and have found that a cast aluminum alloy productcapable of coupling another member therewith by plastic deformation isobtained by addition of Ca, Ti and B to an aluminum alloy with reductionof P content to reform an eutectic phase to fine particles and bycontrol of casting conditions to inhibit occurrence of cast defects andto decrease a difference in average grain size of an α-Al phase grainsize between a surface layer and an inner part of the cast product.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a view for explaining calking a regulator at a cave ofan aluminum alloy product.

[0014]FIG. 2 is a microscopic photograph illustrating a metallurgicalstructure of an aluminum alloy product according to the presentinvention.

[0015]FIG. 3 is another microscopic photograph illustrating ametallurgical structure of an aluminum alloy product having a differentcomposition.

[0016]FIG. 4 is a graph for comparing maximum sizes of segregates inSample No. 1 with Sample No. 9 by image-analysis of metallurgicalstructures.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The composition, the metallurgical structure and themanufacturing conditions specified in the present invention havemeanings explained as follows:

[0018] [Alloying Design]

[0019] Si: 6.5-8.0 mass %:

[0020] Si is an alloying element which precipitates as Mg₂Si, eutecticSi, etc. effective for improvement of mechanical strength andcastability. Such the effect is clearly noted by addition of Si at aratio of 6.5 mass % or more. However, excessive addition of Si above 8.0mass % causes segregation of coarse eutectic Si particles and reducestoughness of a cast alloy.

[0021] Mg: 0.25-0.45 mass %:

[0022] Mg is an alloying element which precipitates as Mg2Si effectivefor improvement of mechanical strength. The effect of Mg on mechanicalstrength is clealy noted by addition of Mg at a ratio of 0.25 mass % ormore. However, excessive addition of Mg above 0.45 mass % causes variousdefects such as inclusion of oxides and poor fluidity during casting.

[0023] Fe: 0.08-0.40 mass %:

[0024] Fe is an alloying element effective for inhibiting burning ofmetal dies. Such the effect is clearly noted by addition of Fe at aratio of 0.08 mass % or more. However, excessive addition of Fe above0.40 mass % causes generation of coarse Al—Fe—Mg—Si intermetalliccompounds, resulting in reduction of toughness.

[0025] Ca: 0.001-0.01 mass % and P: less than 0.0015 mass %:

[0026] The additive Ca with reduction of P content to a possible lowestlevel suppresses generation of primary Si particles and modifieseutectic Si particles, so as to improve a cast aluminum alloy product inductility as well as strength and toughness. The effect of Ca onmodification of eutectic Si particles is clearly noted by addition of Caat a ratio of 0.001 mass % or more (preferably 0.002 mass % or more).However, such the effect is not realized if P content exceeds 0.0015mass %. Fluidity and castability of a molten aluminum alloy are degradedby P content above 0.0015 mass % or addition of Ca above 0.01 mass %.

[0027] 0.02-0.1 mass % Ti and 0.001-0.01 mass % B:

[0028] Ti and B are well-known alloying elements effective forminimization of an α-Al phase grain. In addition to such the effect, theinventors have found from various examinations that Ti and B are alsoeffective for suppressing segregation of an eutectic Si phase if analuminum alloy is cooled at a cooling speed of 20° C./second or higherin a temperature range between liquidus and solidus curves afterinjection into metal dies. The effect on suppression of segregation isclearly noted by addition of Ti at a ratio of 0.02 mass % or more and Bat a ratio of 0.001 mass % or more. However, excessive additions of Tiabove 0.1 mass % and B above 0.01 mass % are likely to cause generationof coarse compounds and to reduce ductility of a cast aluminum alloyproduct.

[0029] One or two of Cr: 0.05-0.3 mass % and Mn: 0.05-0.2 mass %:

[0030] Cr and Mn are optional elements, which are added to an aluminumalloy as occasion demands. Recrystallization, which unfavorably reducesmechanical strength, of a plastically deformed part coupled with anothermember is inhibited by addition of Cr. Such the Cr effect is clearlynoted by addition of Cr at a ratio of 0.05 mass % or more. The additiveMn precipitates as Al(Fe, Mn)Si effective for suppressing generation ofcoarse Al—Fe—Mg—Si intermetallic compounds which put harmful influenceson toughness of a cast aluminum alloy product. Such the Mn effect isclearly noted by addition of Mn at a ratio of 0.05 mass % or more.However, excessive addition of Cr above 0.3 mass % or Mn above 0.2 mass% degrades castability of a molten aluminum alloy.

[0031] [Metallurgical Structure]

[0032] The cast aluminum alloy product according to the presentinvention has the metallurgical structure that an α-Al phase grain in asurface layer from a surface to a depth of 1 mm is differentiated inaverage grain size by 50 μm or less from an α-Al phase grain in an innerpart, a size of eutectic Si particles is controlled at 400 μm orsmaller. Such the small difference in size of α-Al grains between thesurface layer and the inner part as well as the size-control of eutecticSi particles are realized by the specified alloying composition togetherwith control of manufacturing conditions.

[0033] Due to the small difference in size of α-Al grains between thesurface layer and the inner part, the cast aluminum alloy product isgood of ductility without discontinuity of physical properties. The castaluminum alloy product is also plastically deformed for coupling anothermember thereto without occurrence of cracks, since generation of coarseeutectic Si particles acting as origins to start collapse during plasticdeformation is suppressed. If a cast aluminum alloy product containseutectic Si particles above 400 μm in maximum particle size on thecontrary, it can not be used as a protector for a braking systemenclosing a hydraulic circuit therein due to poor cracking resistance,since such coarse eutectic Si particles act as origins for cracking.

[0034] [Casting Conditions]

[0035] After a molten aluminum alloy is adjusted to a predeterminedcomposition, it is injected into a cavity of metal dies by a die-castingprocess. Injection of the molten alloy is performed at a speed of0.05-0.25 m/second. An injection speed of 0.05 m/second or higherensures fluidization of the molten alloy to every nook and corner of thecavity, while an injection speed of 0.25 m/second or less inhibitsoccurrence of blowholes which put harmful influences on airtightness.

[0036] The injected molten alloy is pressed in the cavity with apressure enough to crush blowholes, which are likely to act as originsfor collapse during plastic deformation. Blowholes are effectivelycrushed by application of a pressure of 30 MPa or higher.

[0037] The injected molten aluminum alloy is cooled in the cavity at aspeed of 20° C./second or higher in a temperature range between liquidusand solidus curves. Such the controlled cooling speed in the temperaturerange enables co-presence of Ti and B even after the molten alloyreaches a temperature on the solidus curve, so that Ti and B stilleffectively minimize α-Al grains and suppress segregation of eutectic Siparticles. If the molten alloy is slowly cooled at a speed below 20°C./second, Ti and B are consumed for minimization of α-Al grains inprior to precipitation of the eutectic Si phase. Therefore, the effectof Ti and B on suppressing segregation of eutectic Si particles wouldnot be realized.

[0038] [Coupling Method]

[0039] A molten aluminum alloy is cast to a profile having a cave orhole. Such a cave or hole is easily formed by use of metal dies, whichhas a tubercle or projection extending to a cavity at a positioncorresponding to the cave or hole. For instance, a cast aluminum alloyproduct has a shape partially shown in FIG. 1, wherein a passage 1serving as a part of a hydraulic circuit is formed in a cast aluminumalloy body 2, and a cave 3 is formed at a position where the passage 1opens on a surface of the cast body 2. After a regulator 4 is arrangedin the cave 3 (FIG. 1(a)), a working pressure F is applied to a partabove the cave 3 so as to form a plastically deformed part 5 by metalflow to the cave 3 (FIG. 1(b)). Consequently, the regulator 4 is clampedbetween a bottom of the cave 3 and the plastically deformed part 5.

EXAMPLE

[0040] After a molten aluminum alloy was adjusted to each compositionshown in Table 1, it was degasified and cleaned by removal of slugs. Themolten aluminum alloy prepared in this way was cast to a rectangularparallelepiped shape under conditions indicated in Table 2 by a laminarflow die-casting method. TABLE 1 ALUMINUM ALLOYS USED IN EXAMPLEcomponents (mass %) Alloy No. Si Fe Mg Ti B Mn Cr Ca P 1 7.2 0.25 0.310.02 0.002 <0.01 <0.01 0.0076 0.0007 2 6.9 0.28 0.33 0.05 0.004 0.120.14 0.0082 0.0008 3 7.2 0.27 0.33 <0.01 <0.001 <0.01 <0.01 0.00780.0008

[0041] TABLE 2 CASTING CONDITIONS Present Invention Comparative ExampleCondition No. 1 2 3 4 a temperature (° C.) of metal dies 160 160 160 160a temperature (° C.) of a molten alloy 720 720 720 720 an injectionspeed (m/second) 0.1 0.3 0.1 0.1 a pressure (MPa) during casting 50 5020 50 a cooling speed (° C./second) 30 30 30 10

[0042] After each cast body was solution treated 2 hours at 520° C., itwas quenched in water and then aged 4 hours at 180° C.

[0043] The aged cast body was subjected to observation of itsmetallurgical structure and a mechanical test. In observation of themetallurgical structure, average sizes of α-Al grains in a surface layerfrom a surface to a depth of 1 mm and in an inner part of the cast bodywere measured, and a difference therebetween was calculated. Eutectic Siparticles segregated at boundaries of α-Al grains were also observed tomeasure their maximum particle size. Specific gravity of each die-castproduct together with cast products manufactured by gravity casting thesame aluminum alloys were measured by Archimedes's method. Suppose thatspecific gravity of the die-cast product is a measured value whilespecific gravity of the gravity-cast product is a real value, a porosityof each die-cast product was calculated according to the formula of:a  porosity  (%) = (a  real  specfic  gravity − a  measured  specific  gravity)/a  real  specific  gravity × 100

[0044] Results are shown in Table 3. It is noted that Sample Nos. 1 and5, which had the specified alloying compositions and the metallurgicalstructure controlled according to the present invention, were superiorof tensile strength, yield strength and ductility. There was only asmall difference in size of α-Al grains between a surface layer and aninner part, and a porosity value of Sample No. 1 or 5 was also small.

[0045] Segregation of coarse eutectic particles were not observed, asshown in FIG. 2 which is a microscopic photograph illustrating ametallurgical structure of a cast product obtained by casting thealuminum alloy No. 1 under the casting condition No. 1.

[0046] On the other hand, Sample Nos. 2-4 and 6-8, which were obtainedby casting the same aluminum alloys but under different castingconditions, were poor of ductility and had the metallurgical structuresthat size of an α-Al grains in a surface layer was greatly differentfrom that in an inner part and that eutectic Si particles weresignificantly segregated.

[0047] Sample No. 9, which was obtained by casting the aluminum alloyNo. 3 of different composition under the casting condition No. 1, waspoor of ductility, although a difference in size of α-Al grains betweena surface layer and an inner part was nearly the same level as that ofSample No. 1. When the metallurgical structure of Sample No. 9 wasobserved, segregation of coarse eutectic Si particles was detected, asshown in FIG. 3.

[0048] Maximum diameters of segregates of eutectic Si particles weremeasured by image-analysis of the metallurgical structures (FIGS. 2 and3), and classified to 10 grades. Sizes of segregates at each grade werecompared together, as shown in FIG. 4. It is also recognized in FIG. 4that the segregates in Sample No. 1 (the present invention) were smallerthan those in Sample No. 9 (Comparative Example). TABLE 3 EFFECTS OFALLOYING COMPOSITIONS AND CASTING CONDITIONS ON PROPERTIES ANDMETALLURGICAL STRUCTURES casting tensile 0.2% yield difference maximumsize Sample Alloy condition strength strength Elongation in grainporosity (μm) of eutectic No. No. No. (MPa) (MPa) (%) size (μm) (%) Siparticles 1 1 1 291 243 12.8 <10 0.413 330 2 1 2 287 237 8.7 <40 0.796441 3 1 3 279 240 6.6 <50 0.731 455 4 1 4 294 241 7.8 <40 0.688 478 5 21 293 241 11.6  <5 0.371 328 6 2 2 278 230 7.6 <40 0.881 431 7 2 3 291236 7.3 <50 0.588 454 8 2 4 283 240 6.9 <60 0.534 410 9 3 1 282 236 9.3<10 0.856 579

[0049] 10 test pieces were prepared from every cast product of SampleNos. 1-9 and subjected to a calking test as follows: A regulator 4 wasarranged in a cave 3 of a cast product 2, as shown in FIG. 1(a). Aworking pressure F was applied to a part above the cave 3 to clamp theregulator 4 between a bottom of the cave 4 and a plastically deformedpart 5, as shown in FIG. 1(a). Thereafter, the plastically deformed part5 was inspected to detect occurrence of cracks.

[0050] Results are shown in Table 4. It is apparently noted that any ofSample Nos. 1 and 5 was plastically deformed for coupling the regulator4 without occurrence of cracks. On the other hand, test pieces of SampleNos. 2-4 and 6-9 were often cracked after the plastic deformation. Byobserving a metallurgical structure of the test piece which was crackedafter the plastic deformation, it was recognized that segregates ofcoarse eutectic particles act as origins for cracking. TABLE 4 TENDENCYOF CRACKINGS IN EACH CAST PRODUCT AFTER A CALKING TEST (n = 10) SampleNo. 1 2 3 4 5 6 7 8 9 number of cracked 0 6 8 10  0 6 7 10  8 testpieces

[0051] A cast aluminum alloy product according to the present inventionas above-mentioned, is reformed to such the metallurgical structure thatan average size of α-Al grains in a surface layer is near an averagesize of α-Al grains in an inner part without segregation of coarseeutectic Si particles by addition of Ti, B and Ca with reduction of Pcontent. Due to the reformed structure, the cast product can beplastically deformed by calking or the like for coupling another membertherewith. Therefore, the cast product is useful in various technicalfields, instead of an expensive ductile aluminum alloy which has beenused so far for such the purpose. The cast product is also superior ofairtightness, so useful as a protector for an automobile braking systemenclosing a hydraulic circuit therein.

1. A plastically worked cast aluminum alloy product, which comprises acomposition consisting of 6.5-8.0 mass % Si, 0.25-0.45 mass % Mg,0.08-0.40 mass % Fe, 0.001-0.01 mass % Ca, P less than 0.0015 mass %,0.02-0.1 mass % Ti, 0.001-0.01 mass % B, optionally one or two of0.05-0.3 mass % Cr and 0.05-0.2 mass % Mn, and the balance being Alexcept inevitable impurities; and has a metallurgical structure whereinan α-Al phase grain in a surface layer from a surface to a depth of 1 mmhas average grain size different by 50 μm micron or less from an α-Alphase grain in an inner part, and a maximum particle size of an eutecticSi phase is less than 400 μm.
 2. A method of manufacturing a ductilecast aluminum alloy product, which comprises the steps of: preparing amolten aluminum alloy having a composition consisting of 6.5-8.0 mass %Si, 0.25-0.45 mass % Mg, 0.08-0.40 mass % Fe, 0.001-0.01 mass % Ca, Pless than 0.0015 mass %, 0.02-0.1 mass % Ti, 0.001-0.01 mass % B,optionally one or two of 0.05-0.3 mass % Cr and 0.05-0.2 mass % Mn, andthe balance being Al except inevitable impurities; injecting said moltenalloy into a cavity of metal dies at a speed of 0.05-0.25 m/second; andcooling said injected molten alloy at a cooling speed of 20° C./secondor higher in a temperature range between liquidus and solidus curves ofsaid aluminum alloy in a state charged with a pressure of 30 MPa ormore.
 3. A method of coupling a cast aluminum alloy product with anothermember using plastic deformation, which comprises the steps of:preparing a molten aluminum alloy having a composition consisting of6.5-8.0 mass % Si, 0.25-0.45 mass % Mg, 0.08-0.40 mass % Fe, 0.001-0.01mass % Ca, P less than 0.0015 mass %, 0.02-0.1 mass % Ti, 0.001-0.01mass % B, optionally one or two of 0.05-0.3 mass % Cr and 0.05-0.2 mass% Mn, and the balance being Al except inevitable impurities; injectingsaid molten alloy into a cavity of metal dies at a speed of 0.05-0.25m/second, so as to shape a cast body to a profile having a cave or hole;cooling said injected molten alloy at a cooling speed of 20C./second orhigher in a temperature range between liquidus and solidus curves ofsaid aluminum alloy in a state charge d with a pressure of 30 MPa ormore; arranging another member in said cave or hole of said cast body;and coupling said another member to said cast body by plastic flow of analloy at a part above or around said cave or hole to said cave or hole.